1. Field of the Invention
The present invention relates to metallic structures, and more particularly, to mixed-metal structures for use in metal enhanced emission systems to enhance emissions from fluorophores, luminophores, bioluminescent species, chemiluminescent species and light emitting devices.
2. Background of the Related Art
In the last decade the interaction of fluorophores with metallic nano-particles has attracted significant literature (1-5), with numerous applications focused at the life sciences (2, 6-9). Fluorophore near-field interactions with plasmon supporting materials typically leads to enhanced fluorescence signatures (3, 5, 10, 11), and reduced fluorophore lifetimes, which, invariably lends itself to enhanced fluorophore photostabilities. Enhanced Chemiluminescence signatures (12), as well as enhanced triplet yields have also been reported from different metallic surfaces (13), with enhanced triplet yields giving rise to a variety of favorable reactive oxygen photophysics, such as enhanced singlet oxygen and superoxide anion radical generation (14, 15). The wavelength dependence of metal enhanced fluorescence (MEF) has also recently been postulated (16), as well as the angular dependence of emission (17), the distance dependence of MEF (18, 19), as well as excitation volumetric effects (EVE) (20), which readily allows for tunable luminescence enhancement factors. Since MEF was defined nearly a decade ago (3) and the mechanism postulated only a few years later (21), nearly all the reports of MEF have involved the exclusive use of single metallic substrates. Several reports of mixed metal continuous film coatings for SPCF and particularly substrates utilizing dielectric coatings or spacer layers e.g. SiO2 and SiOx, can be found in the research literature (22, 23). There is also a significant literature on the plasmonics properties of metal-metal coatings, such as Halas et al (24, 25), although none of these reports involve near-field dipoles and enhanced fluorescence signatures.
Notably, these studies have been focused on one single metal structure including a single metal such as Silver Island Films (SiFs) and provide no ability to provide mixed metal structures that can be used to enhance fluorescence as compared to the individual metal substrates alone. Thus it would advantageous to provide metallic particles that include mixed metals to provide increased intensity of fluorescence and photostability.